A special-purpose colorimeter is being developed to evaluate the results of ELISA (Enzyme-Linked Immuno Sorbent Assay) tests on small samples. The ELISA test is a simple and safe test for the detection of antibodies and antigens in fluids from human beings. The result of the ELISA test is detectable as an optical density change at a wavelength of either 400 nm or 490 nm, depending on the chemistry of the test. The system allows the chemistry and the final analysis to be performed in the same 96-well microtiter tray, and the sample can be preserved after the test is completed, if desired, for further evaluation. A prototype unit, inexpensive to build and simple to operate, is presently being used. BIBLIOGRAPHIC REFERENCE: Yolken, R., Kim, H., Clem, T., Wyatt, R., Kalica, T., Chanock, R. and Kapikian, A.: Enzyme immunoassay (ELISA) for the detection of human reovirus-like agent in human stools. Lancet II: 263-266, 1977.